Method of replacing deactivated catalyst in expanded bed process



Sept. 21, 1965 R. P. VAN DRIESEN 3,207,689

METHOD OF REPLACING DEACTIVATED CATLYST IN EXPANDED BED PROCESS FiledJune 7, 1965 PRODUCT INVENTOR ROGER P. VANDRElsl-:N

HYDROGEN ATTORNEY United States Patent C 3,207,689 METHQD F REPLACENGDEACTHVATED CAT- ALYST IN EXPANDED BED PRCESS Roger P. Van Driesen,Hopewell, N5., assigner, by mesne assignments, to Cities ServiceResearch and lilevelopment Company, a corporation of Delaware Filed.lune 7, 1963, Ser. No. 288,852

4 Claims. (Cl. ZllS-ISZ) This application is a continuation-impart of mycopending application S.N. 121,436, filed July 3, 1961y now abandoned,for Catalyst Replacement.

This invention relates to catalytic treatment of liquid and moreparticularly to replenishment of catalyst in a process for the catalytictreatment of liquid in which upilowing liquid maintains a bed of nelydivided catalyst in an expanded condition. The invention has particularapplication to processes such as hydrogenation in which liquidhydrocarbon oil is contacted with catalyst which becomes at leastpartially deactivated over a period of time.

The present invention is applicable to any system in which liquid istreated with an expanded bed of catalyst and it is desired to replacecatalyst which has been in the treating vessel the longest period oftime. In such processes, liquid or a mixture of liquid and gas is passedupwardly through a bed of catalyst particles at a sucient velocity toexpand the volume of the catalyst bed and cause random movement ofcatalyst particles but at an insuilicient velocity to cause generalupward movement or carry over of the catalyst from the bed. Bedexpansion in such instances is normally between about and about 300percent based on the unexpanded volume of the catalyst. In such anexpanded bed the catalyst particles are not lixed but `are in a state ofrandom motion induced by the velocity of the upowing fluid. This motionallows a very efficient contact between fluid and catalyst to takeplace. Such movement is, however, limited to the extent that the violentslugging and mixing typical of a bed of finely divided catalystfluidized by gas does not take place and the upper portion of theexpanded bed of catalyst is usually sharply defined. It has now beenfound that in such catalyst beds expanded by fluid ow, relatively largercatalyst particles tend to form the lower portion of the catalyst bedwhile relatively smaller particles tend to form the upper portion of thebed.

In catalytic reactions in which fluid is passed upwardly through anexpanded bed of catalyst particles as described above, such as in thetreatment of liquid hydrocarbon oil with hydrogen in contact with suchan expanded bed of catalyst, it is necessary, due to normal deactivationor contamination of the catalyst, to replace the catalyst from time totime. This may, of course, be accomplished by replacing the entirecatalyst inventory at once or may be accomplished by continuous orintermittent withdrawal of partially spent catalyst and replacement withfresh catalyst. Unfortunately, in conventional methods for replacingcatalyst, the catalyst Withdrawal is necessarily a representative sampleof all the catalyst present in the catalyst bed and contains some freshas well as some spent catalyst. It is, therefore, an object of thepresent invention to provide a method for replacing catalyst in systemsof the type described above in which the 3,2il789 Patented Sept.. 21,1965 relatively older and therefore more deactivated catalyst isselectively removed.

ln accordance with the present invention, catalyst maintained in anexpanded bed by upflowing liquid may be partially replaced bywithdrawing catalyst from the lower portion of the bed and addingcatalyst of a smaller particle size to the upper portion of the bed orby withdrawing catalyst from the upper portion of the bed and addingcatalyst of a relatively larger particle size to the lower portion ofthe bed. Due to the tendency of the different particle sizes to remainseparated in the expanded bed, the freshly added catalyst is not to anysubstantial extent mixed with the older catalyst of different particlesize and hence is not withdrawn during subsequent Withdrawal of furtherportions of the older catalyst.

When catalyst of the original size has been substantially replaced bythe different sized .catalyst being added, the process may be reversedand catalyst of the original size again added as the fresh catalyst. Forinstance, if as described above, relatively larger catalyst is Withdrawnfrom the lower portion of the catalyst bed and relatively smallercatalyst added to the upper portion thereof, then when the relativelylarger catalyst has been replaced by the relatively smaller catalyst,the process may be reversed and relatively larger catalyst added to thelower portion of the catalyst bed while the relatively smaller catalystis withdrawn from the upper portion thereof. This will eventually leadto a condition in which the catalyst bed consists `substantially of therelatively larger catalyst of the same size as was originally presentand the entire process may then be repeated `any desired number of timeswith the composition of the catalyst bed changing from mostly relativelylarge sized catalyst to mostly relatively small `sized catalyst and backagain. In this manner the advantages of the invention may be obtainedover many changes of catalyst and the overall catalyst consumption ratefor the process will be drastically reduced.

For a better understanding of the invention reference should be had tothe accompanying drawing which is a somewhat diagramatic illustrationwith equipment shown in elevation of a suitable arrangement of apparatusfor carrying out a preferred embodiment of the invention in conjunctionwith the hydrogenation of hydrocarbon oil.

Referring to the dawing, feed oil entering through a conduit 11 andvalve l2 and hydrogen entering through a conduit 13 and valve 14 arepassed through the conduit 13 into the lower portion of a hydrogenationreactor 16. The reactor 16 contains a bed of finely dividedhydrogenation catalyst which is maintained in an expanded condition byupward flow of liquid and hydrogen through the reactor. ln the drawing,this hydrogenation catalyst is shown in the form of relatively largerparticles which form a lower portion 17 of the expanded bed of catalystand relatively smaller particles which form an upper portion 18 of theexpanded bed of catalyst. Liquid and gaseous product is Withdrawn fromthe reactor as through a conduit 23 and valve 24. When it is desired toreplace a portion of the catalyst, larger catalyst may be withdrawn fromthe lower portion of the catalyst bed as through a conduit 21 and valve22 while fresh, smaller catalyst may be added to the upper portion ofthe catalyst bed as through a conduit 19. It is readily apparent thatreplacement of catalyst in this manner results in selective withi drawalof the relatively larger, older catalyst until substantially the entirecatalyst bed is composed of the relatively smaller catalyst. In thismanner it is possible to avoid withdrawal of excessive amounts ofrelatively fresh catalyst as would otherwise occur if the withdrawncatalyst were a representative sample of the entire catalyst inventoryin the reactor.

While the catalyst and operating conditions discussed herein relateespecially to treatment of hydrocarbon oil with hydrogen, it should beunderstood that replacement of catalyst in any process for the catalytictreatment of liquid in which the catalyst is maintained in an expandedbed of the type described is within the scope of the invention.

The catalyst employed in the reactor 16 may be any suitablehydrogenation catalyst such as cobalt, iron, molybdenum, nickel,tungsten or cobalt molybdate. Such catalysts as well as their sulfidesand oxides may be used alone or together with other suitable catalystsor in combination with each other and all such catalysts may, of course,be supported on suitable bases such as alumina, silica or alumina-silicagel. Such catalyst is present in the form of finely divided particleshaving a suitable size such as between about 1/100 and 1%; of an inchwith particle sizes on the order of 1&4 to lAG of an inch being moreusual. In the practice of the present invention it is necessary that thecatalyst in the reactor 16 be expanded to a volume greater than itssettled volume by the upward fiow of liquid through the reactor. Suchbed expansion is preferably at least about percent and may be as much asabout 300 percent based on the settled volume of the catalyst. Theupward velocity of fluid necessary to accomplish the desired expansionwill, of course, depend upon the size and density of catalyst particlesused as well as the properties of the uid flowing upwardly through thereactor. For any given process, it is a relatively simple matter todetermine the particular velocity which will cause the catalyst bed tobecome expanded to the desired extent. As mentioned above such expansionof the catalyst bed results in random motion of the catalyst particleswithout the somewhat more violent mixing which occurs in catalyst bedsfluidized by gas. Expansion of the catalyst bed by liquid as describedabove allows such random motion without any substantial amount ofcatalyst being carried upwardly above the upper level of the bed and theupper level of the bed is usually fairly well defined. Due to the abovementioned random motion of catalyst particles unaccompanied by Violentmixing, relatively larger particles of the same catalyst tend to remainin the lower portion of the catalyst bed such as the portion 17 of thebed shown in the drawing while relatively smaller catalyst particlestend to form the upper portion of the catalyst bed such as the upperportion 18 of the bed shown in the drawing. While the upward velocity ofiluid within the reactor needed to obtain the desired amount of bedexpansion will vary widely as discussed above, velocities on the orderof 20 to 120 gallons per minute per square foot of reactor crosssectional area are frequently used.

The feed introduced through the conduit 11 as described above may be anysuitable hydrocarbon oil and may vary considerably depending upon theparticular hydrogenation reaction desired. Hydrogenation reactions may,for instance, vary from relatively mild treatment under relatively lowerconditions of temperature and pressure to more severe treatments underrelatively higher conditions of temperature and pressure. Mild treatmentmay be used to achieve improved color or stability and is frequentlyused to treat relatively light oils such as gas oil while more severetreatment may be used to effect hydrodesulfurization or hydrocrackingand is more usually practiced on heavier feeds such as residualfractions.

The space velocity in the reactor 16 may vary widely such as betweenabout 0.5 and about 5.0 volumes of feed per hour per volume of reactorcapacity. The space i velocity, like the other operating conditionsmentioned herein is not, however, completely independent and must beselected with other desired conditions in mind.

Hydrogen is introduced through the conduit 13 in quantities suitable tothe particular hydrogenation reaction taking place in the reactor 16 andmay, for instance, be introduced at rates between about 2,500 and about10,000 standard cubic feet per barrel of feed. Likewise, the temperatureat which the reactor 16 is maintained will vary widely depending uponthe particular reaction taking place as well as upon the feed and othervariables with temperatures between about 600 F. and about 900 F. beingcommonly used. The temperature of the reactor 16 may be maintained inany suitable manner such as by controlling the temperature of the feedentering through conduit 11. The reactor 16 may be maintained under anysuitable pressure such as between about 1,500 and about 4,000 p.s.i.g.partial pressure of hydrogen.

As shown in the drawing, catalyst may be replaced in accordance with thepresent invention by withdrawing relatively larger catalyst from thelower portion of the expanded bed of catalyst and adding relativelysmaller catalyst to the upper portion thereof. While the difference insize between the relatively larger and relatively smaller catalyst may,of course, vary quite widely, it is possible that if the difference insize is too small an undesirable amount of mixing between the twodifferent sizes of catalyst will take place while if the difference incatalyst sizes is too large it may become difiicult to find a velocitycapable of expanding both catalyst sizes approximately the desiredamount. In general, it is, therefore, preferred that the relativelylarger catalyst particles be between about 5/4 and about 3 times thesize of the relatively smaller catalyst.

EXAMPLE The following specific example illustrates the practicalapplication of the present invention using the process and apparatusdescribed above and shown in the drawing in the hydrocracking of a heavyresidual oil.

In this example the `feed is a West Texas long residual having a gravityof 16.3 API and containing 2.6 weight percent sulfur. This feed isintroduced through the conduit 11 while hydrogen is introduced throughthe conduit 12 .at the rate of 6,000 standard cubic feet per barrel offeed. The catalyst employed in the reactor 16 is cobaltmolbydenumhydrogenation catalyst on an alumina base. The catalyst initiallypresent in the reactor at the start of the process has a particle size.of 1/16 inch. The reactor 16 is maintained under a hydrogen partialpressure of 2,000 p.s.i.g. and a temperature of 820 F. The spacevelocity is about 3.0 volumes of feed per hour per volume of reactorspace. Liquid is passed upwardly through the reactor 16 at the rate of75 gallons per minute per square foot of reactor cross sectional area,thereby expanding the bed of catalyst by about 50 percent based on thesettled volume of the catalyst. After the unit has been on stream for 50days, replacement of catalyst is begun by continuously orsemi-continuously withdrawing catalyst from the lower portion of thecatalyst bed through the conduit 21 and valve 22 and yreplacing thuswithdrawn catalyst with fresh catalyst having a particle size of j/32 ofan inch introduced through conduit 19 into the upper portion of thecatalyst bed. Such catalyst addition and withdrawal is `continued at arate sufficient to maintain the average age of catalyst in the reactor16 at 50 days. Under these conditions the liquid product removed throughconduit 23 has a gravity of 25 API and contains 0.6 weight percentsulfur. Product yield is 102 volume percent based on feed.

Table I below demonstrates more clearly the benefit to be gained byreplacing catalyst as described above rather than by withdrawing arepreseitative mixture of all catalyst in the reactor in accordance withnormal procedure.

Table LCatal'yst' replacement rale using' fwo catalyst sizes with dailyreplacement to maintain an average age of days Larger catalyst Smallercatalyst Percent Days on of total Av. age stream Percent Percent cat.tot. cat. Age of total Av. age of total replaced catalyst catalyst 50 50100. 0 0 0 0. 0 50 51 51 9B. 0 0 2. 0 2. 0 49. 98 52 52 96. 0 0. 5 4. 02. 0 49.94 53 53 94. 0 1. D 6. 0 2. 0 49. 88 54 54 92. 1 1. 52 7. 9 1. 949.85 55 55 90. 3 2.05 9. 7 1. 8 49. 87 56 56 88. 6 2` 60 11. 4 l. 749.92 57 57 87. 0 3. 16 13. 0 1. 6 50. 00 58 58 85.4 3. 70 14. 6 1. 650. 07 59 59 83. 8 4. 23 16.2 1. 6 50. 13 60 60 82. 2 4. 76 17. 8 1.650. 17 61 61 80. 6 5. 29 19. 4 1. 6 50. 20 62 62 79. 0 5. 81 21. 0 1. 650. 20 63 63 77. 4 6. 33 22.6 1. 6 50.19 64 64 75. 8 6. 85 24. 2 1. 650. 17 65 65 74. 2 7. 36 25.8 1. 6 50. 13 66 66 72. 6 7. 88 27. 4 1. 650. 08 67 67 71.1 8. 42 28.9 1. 5 50.07 68 68 69. 6 8. 96 30. 4 1. 5 50.05 69 69 68. 2 9. 52 31.8 1. 4 50. 09 70 70 66. 8 10. 08 33. 2 1` 4 50.11 71 71 65. 4 10. 63 34.6 1. 4 50.11 72 72 64. 0 11. 18 36.0 1. 4 50.10 73 73 62. 6 11.72 37. 4 1. 4 50. 08 74 74 61.2 12. 26 38. 8 1. 4 50.05 75 75 59. 9 12.83 40. 1 1. 3 50. 07 76 76 58. 6 13. 40 41. 4 1. 350.09 77 77 57. 3 13. 96 42. 7 1. 3 50.08 78 78 56. 0 14. 52 44. 0 1. 350. 07 79 79 54. 7 15. 07 45.3 1.3 50. 04 80 80 53. 4 15. 62 46. 6 1. 350. 00 81 81 52. 2 16. 20 47. 8 1. 2 50. 02 82 82 51. 0 16. 78 49. 0 1.2 50. 04 83 83 49.8 17.35 50.2 1. 2 50.04 84 84 48. 6 17.92 51. 4 1. 250. 03 85 85 47. 4 18. 49 52. 6 1. 2 50. 02 86 86 46.2 19.06 53. 8 1. 249.98 87 87 45. 1 19.66 54.9 1.1 50. 03 88 88 44. 0 20. 26 56.0 1.150.07 89 89 42. 9 20. 85 57. 1 1. 1 50. 09 90 90 41.8 21.44 58. 2 1. 150.10 91 91 40. 7 22. 02 59. 3 1. 1 50. 10 92 92 39. 6 22. 60 60. 4 1. 150.08 93 93 38. 5 23. 18 61.5 1.1 50.07 94 94 37. 4 23. 75 62. 6 1. 150. 03 95 95 36.3 24. 32 63. 7 1.1 49. 98 96 96 35. 2 24.89 64. 8 l. 149. 92 97 97 34.2 25. 50 65. 8 1. 0 49.95 98 98 33. 2 26.10 66.8 1.0 49.97 99 99 32. 2 26.70 67. 8 l. 0 49.98 100 100 31. 2 27. 30 68. 8 1.049.98 101 101 30. 21 27. 90 69. 79 0. 99 49.98 102 102 29. 23 28. 50 70.77 0. 98 49.98 103 103 28. 3 29. 12 71. 7 0. 93 50. 03 104 104 27. 429.75 72. 6 0. 90 50. 10 105 105 26. 5 30. 37 73. 5 0. 90 50. 15 105 10625. 6 30. 99 74. 4 0. 90 50. 20 107 107 24. 7 31. 61 75. 3 0. 90 50. 23108 108 23.8 32. 23 76. 2 0. 90 50. 26 109 109 22. 9 32. 84 77. 1 0. 9050. 28 110 110 22.0 33. 45 78. 0 0. 90 50.29 111 111 21. 1 34.06 78` 90.90 50.29 112 112 20.2 34.66 79. 8 0.90 50.28 113 113 19. 3 35.26 80. 70.90 50.26 114 114 18. 4 35. 86 81. 6 0. 90 50. 24 115 115 17. 5 36. 4582. 5 0. 90 50. 20 116 116 16. 6 37. 05 83. 4 0. 90 50. 16 117 117 15.737. 64 84. 3 0.90 50. 10 118 118 14.8 38, 23 85. 2 0.90 50.03 119 11913.9 38. 82 86.1 0.90 49.96 120 120 13. 0 39. 51 87. 0 0. 90 49. 97 121121 12. 1 40. 10 87. 9 0. 90 49. 89 122 122 11. 2 40. 68 88. 8 0. 90 49.78 123 123 10. 3 41. 26 89.7 0. 96 49. 68 124 124 9. 5 41. 89 90. 5 0.8049. 69 125 125 8. 7 44. 51 91. 3 0. 80 49. 69 126 126 7. 9 43. 13 92. 10. 80 49. 67 127 127 7. 2 43. 80 92. 8 0. 70 49. 79 128 128 6. 5 44. 4693. 5 0.70 49. 89 129 129 5. 8 45. 12 94. 2 0. 70 49. 98 130 130 5. 145. 78 94. 9 0. 70 50. 08 131 131 4. 4 46. 44 95. 6 0. 70 50. 16 132 1323. 7 47. 09 96. 3 0. 70 50` 23 133 133 3. 0 47. 74 97. 0 0. 70 50.30 134134 2. 2 48. 34 97. 8 0.80 50. 23 135 135 1. 4 48. 94 98. 6 0. 80 50. 14136 136 0. 7 49. 59 99. 3 0.70 50. 19 137 137 0. 0 50. 24 100. 0 0. 7050. 24

Total days to replace catalyst charge using two sizes 86 Total days toreplace catalyst charge using one size with completing mixing 50Catalyst consumption using two sizes/ catalyst consumption using onesize 0.575

From Table I it is apparent that with selective withdrawal of relativelyolder and therefore more deactivated catalyst and replacement with freshcatalyst by making use of the tendency of relatively larger catalyst toform the lower portion of an expanded catalyst Ibed and relativelysmaller catalyst to form the upperl portion thereof, the total amount offresh catalyst required to maintain catalyst activity is substantiallyreduced. Specifically, Table I shows that in the example given above thetotal catalyst charge need be replaced only once each 86 days tomaintain an average catalyst life of 50 days. By contrast, if thewithdrawn catalyst is a representative sample of the total catalystinventory in accordance with conventional practice, than a total freshcharge of catalyst must be added every 50 days. Catalyst -consumptionutilizing the present invention is, therefore, only a little more thanhalf `of the catalyst consumption using only one size of catalyst inaccordance with conventional practice.

While the invention is described herein in conjunction with a process inwhich relatively larger catalyst is withdrawn from the lower portion ofan expanded bed of catalyst and relatively smaller catalyst is added tothe upper portion thereof, it will be understood that numerousvariations of this process are within the scope of the invention. Forinstance, it is equally feasible to withdraw relatively smaller catalystfrom the upper portion of the expanded bed and add relatively largercatalyst to the lower portion thereof. It is also, of course, feasibleto utilize a process of the type described herein as one stage in amulti-stage treatment process.

It is also, as described above, possible to obtain the advantages of theinvention on a continuous basis through many changes of catalyst byalternating addition of relatively larger and relatively smallercatalyst so that the composition of the catalyst bed is constantlychanging from mostly one sized catalyst to mostly the other sizedcatalyst. For instance, in the above example, after the relrelativelylarger lAf; in. catalyst has been substantially completely replaced withthe relatively smaller 1/32 in. catalyst, the process may be reversedwith the smaller 1&2 in. catalyst being withdrawn from the upper portionof the catalyst bed and the larger 1;/16 in. catalyst being added to thelower portion thereof. Then after the catalyst bed is again composedmostly of the larger 1/16 in. catalyst, withdrawal of the largercatalyst and addition of the smaller catalyst may again take place. Thisprocess may, of course, be repeated as many times as desired and thebenefits of low catalyst consumption as outlined above will bemaintained for so long as addition and Withdrawal in this manner iscontinued.

It will also be apparent to those skilled in the art that various otherchanges and modifications may be made without departing from the spiritand scope of the invention and it is intended to cover all such changesand modifications in the appended claims.

I claim:

1. In a process for the treatment of hydrocarbon oil in which liquidhydrocarbon oil is passed upwardly through a bed of catalyst particlesat a velocity sucient to expand the volume of said bed of catalystbetween about 10 and about 300 percent based on the unexpanded volume ofthe bed and in which said catalyst becomes at least partiallydeactivated, the method of replacing thus deactivated catalyst whichcomprises withdrawing catalyst of a relatively larger average particlesize from a lower portion of said bed and adding catalyst of arelatively smaller average particle size to' an upper p0rtion of saidbed until the majority of the catalyst of said relatively larger averageparticle size has been replaced with said catalyst of relatively smallerparticle size, and then withdrawing catalyst of a relatively smalleraverage particle size from an upper portion of said bed and addingcatalyst of a relatively larger average particle size to a lower portionof said bed until the majority of the catalyst of said relativelysmaller average particle size has been replaced by said catalyst ofrelatively larger average particle size, the particles of said catalystof relatively larger particle size being in each case between about 5/4and about 3 times the size of the particles of said catalyst ofrelatively smaller particle size and said catalyst in each case havingan average particle size be tween about 1/100 and about l; of an inch.

2. In a process for the treatment of hydrocarbon oil in which liquidhydrocarbon oil is passed upwardly through a bed of catalyst par-ticlesat a velocity sufficient to expand the volume of said bed of catalystbetween about 10 and about 300 percent based on the uneXpanded volume ofthe bed and in which said catalyst becomes at least partiallydeactivated, the method of replacing thus deactivated catalyst whichcomprises withdrawing catalyst of a relatively smaller average particlesize from an upper portion of said bed and adding catalyst of arelatively larger average particle size to a lower portion of said beduntil the majority of the catalyst of said relatively smaller averageparticle size has been replaced with said catalyst of relatively largerparticle size, and then withdrawing catalyst of a relatively largeraverage particle size from a lower portion of said bed and addingcatalyst of a relatively smaller average particle size to an upperportion of said bed until the majority of the catalyst of saidrelatively average particle size has been replaced by said catalyst ofrelatively smaller average particle size, the particles of said catalystof relatively larger particle size being in each case between about 5/4and about 3 times the size of the particles of said catalyst ofrelatively smaller particle size and said catalyst in each case havingan average particle size between about 1/100 and about Ms of an inch.

3. The method of replacing at least partially deactivated catalyst in abed of finely divided catalyst particles maintained in an expandedcondition by movement of fluid upwardly therethrough which compriseswithdrawing at least partially deactivated catalyst of a relativelylarger average particle size from a lower portion of said bed and addingcatalyst of a relatively smaller average particle size to an upperportion of said bed, and then withdrawing catalyst of a relativelysmaller average particle size from an upper portion of said bed andadding catalyst of a relatively larger average particle size to a lowerportion of said bed.

4. The method of replacing at least partially deactivated catalyst in abed of finely divided catalyst particles maintained in an expandedcondition by movement of fluid upwardly therethrough which compriseswithdrawing at least partially deactivated catalyst of a relativelysmaller particle size from an upper portion of said bed and addingcatalyst of a relatively larger particle size to a lower portion of saidbed, and then withdrawing catalyst of a relatively larger averageparticle size from a lower portion of said bed and adding catalyst of arelatively smaller average particle size to an upper portion of saidbed.

References Cited by the Examiner UNITED STATES PATENTS 2,706,167 4/55Harper et al. 208-264 2,910,433 10/59 Pichler 208-216 2,987,467 6/61Keith et al. 208-216 2,987,468 6/61 Chervenak 208-217 ALPHONSO D.SULLIVAN, Primary Examiner.

1. IN A PROCESS FOR THE TREATMENT OF HYDROCARBON OIL IN WHICH LIQUIDHYDROCARBON OIL IS PASSED UPWARDLY THROUGH A BED OF CATALYST PARTICLESAT A VELOCITY SUFFICIENT TO EXPAND THE VOLUME OF SAID BED OF CATALYSTBETWEEN ABOUT 10 AND ABOUT 300 PERCENT BASED ON THE UNEXPANDED VOLUME OFTHE BED AND IN WHICH SAID CATALYST BECOMES AT LEAST PARTIALLYDEACTIVATED, THE METHOD OF REPLACING THUS DEACTIVATED CATALYST WHICHCOMPRISES WITHDRAWING CATALYST OF A RELATIVELY LARGER AVERAGE PARTICLESIZE FROM A LOWER PORTION OF SAID BED AND ADDING CATALYST OF ARELATIVELY SMALLER AVERAGE PARTICLE SIZE TO AN UPPER PORTION OF SAID BEDUNTIL THE MAJORITY OF THE CATALYST OF SAID RELATIVELY LARGER AVERAGEPARTICLE SIZE HAS BEEN REPLACED WITH SAID CATALYST OF RELATIVELY SMALLERPARTICLE SIZE, AND